The present invention relates to a flat-running device intended for equipping a mounted assembly without an air chamber for a motor vehicle having a multi-block wheel rim, and to such a mounted assembly incorporating this device and making it possible to cover a long distance at relatively high speed when the mounted assembly is partially or completely deflated. This flat-running device can be used particularly for equipping a military vehicle intended for traveling on all types of ground, including sandy ground.
The known flat-running devices for mounted assemblies comprising a multi-block rim conventionally comprise:                an annular supporting structure which is intended to be mounted around the rim for the purpose of supporting the flat-running tire and which is divided into a plurality of ring sectors in the form of an arc of a circle placed end to end in the circumferential direction, and        means for locking the beads against the rim flanges, as is described, for example, in the document EP-A-1 900 551 in the name of the Applicant.        
In this document, these sectors are surmounted by a rubber-based tire support casing which projects axially on either side of the lateral faces of the supporting structure, at the same time covering them partially, and which is designed, in particular, to protect this structure in a flat-running situation and the tire when it is running in the inflated state.